The present invention relates to an unmanned vehicle guide system and, more particularly, to a structure of an intersection of guide routes comprising a magnetic material.
Recently, in factories, warehouses, hospitals, offices, and so on, an unmanned vehicle that moves on a guide route provided on a floor by control of a computer has been widely used.
In a well known unmanned vehicle guide system, an electromagnetic induction cable or a marker such as a light-reflecting plate, a belt-like metal plate, a magnetic material, and so on is provided along a travel route. In any such system, a factor to destabilize travel of an unmanned vehicle exists at a portion (to be referred to as an intersection hereinafter) where guide routes branch, merge, or intersect.
For example, in a guide system using an electromagnetic induction cable, in order to prevent electromagnetic interference between cables at an intersection of guide routes, currents of different frequencies are flowed in a plurality of cables, respectively. An unmanned vehicle selects by detecting only a cable having a designated frequency so that it switches to a desired direction at an intersection. With such a guide route comprising a plurality of cables in which currents of different frequencies are flowed, it is difficult to obtain a complex route course. Furthermore, since the cables are buried in the floor, it is difficult to change the cable layout.
In a guide system using a light-reflecting plate such as an aluminum foil, an unmanned vehicle is switched by detecting a marker provided in the vicinity of an intersection of guide routes or by optically detecting an intersection by utilizing the large width of a guide route at the intersection. Since marker installation is easy, it is easy to change the guide route layout However, since a damaged or soiled portion of the light-reflecting plate constituting the guide route causes noise, off-the-route or unstable travel occurs, and maintenance becomes cumbersome.
In a guide system (to be referred to as a magnetic guide system hereinafter) as an object of the present invention wherein a guide route comprises a magnetic material, the guide route is made by a magnetic material such as iron powder or ferrite. The unmanned vehicle has a magnetic sensor including a single exciting coil, for exciting a magnetic field over the magnetic guide, and a pair of detection coils, arranged on two sides of the exciting coil along a direction perpendicular to the travel direction of the unmanned vehicle, for detecting a magnetic field change due to the guide. The sensor further includes a comparator for obtaining a difference between the output voltages of the pair of detection coils, and an amplifier for amplifying an output from the comparator. An output from the amplifier is supplied to a steering motor that determines the travel direction of the unmanned vehicle. U.S. patent application Ser. No. 796,209 filed by the present applicant clearly describes the actual structure of the guide system.
FIGS. 1A and 1B show the guide principle of the magnetic guide system.
FIG. 1A shows a magnetic sensor S attached to an unmanned vehicle and a magnetic guide 4 extending in the Y-direction (perpendicular to the surface of the sheet of the drawing), and indicates sensor components, exciting coil E and a pair of detection coils A and B. Circles M drawn in broken lines represent a magnetic field emitted from the exciting coil E. The unmanned vehicle runs along the guide 4 fixed on the floor, by an automatic steering not to deviate in the X-axis direction (arrow L or R).
Referring to FIG. 1B, the abscissa corresponds to the X-axis of FIG. 1A, curves 11 and 12 respectively indicate a change in the voltage output of the detection coils A and B with respect to the lateral deviation of the unmanned vehicle in the X-axis direction, and a curve 13 indicates a difference between the output voltages 11 and 12 (the curves 11 and 12).
When the unmanned vehicle swings to the right or left during travel, the difference voltage changes along the curve 13 and becomes 0 when the unmanned vehicle comes just above the guide 4. Namely, the unmanned vehicle steers automatically such that the difference voltage 13 (the curve 13) keeps 0 V.
In the magnetic guide system, no electric power is required for the guide route, and, moreover, the control of the unmanned vehicle is not influenced by the damaged or soiled portion of the guide route. Also, since the guide route can be obtained only by adhering or coating a magnetic material, its installation or layout change can be easily performed.
However, the following problem arises at an intersection of the guide routes
FIGS. 2 and 3 show a defect at an intersection of guide routes of a conventional magnetic guide system.
FIG. 2 shows a three-forked intersection of a guide 4. An alternate long and short dashed line 1 indicates a travel track (to be referred to as a 0-V line hereinafter) at which the sensor output voltage 13 becomes 0 during the unmanned vehicle travelling on the guide 4 in a direction of arrow 3. In FIG. 2, a solid curve 15 and a broken line 16 represent travel tracks of the unmanned vehicle at which the sensor output voltage 13 becomes maximum and minimum, respectively.
FIG. 3 shows a 0-V line 1 of a cross intersection.
As apparent from FIGS. 2 and 3, since the width of the magnetic material constituting the guide 4 is large at the intersection, the unmanned vehicle is influenced by a change in the magnetic profile, and the 0-V line goes zig-zag. As a result, the unmanned vehicle steered to travel along the 0-V line starts travelling in a zig-zag manner and may travel off the route when the vehicle speed is high.
FIG. 4 shows an example of countermeasures conventionally provided to prevent off-the-route travel of an unmanned vehicle caused by zig-zag travelling. Referring to FIG. 4, a marker 17 made of a metal or a magnetic material is arranged in the vicinity of an intersection. The unmanned vehicle is provided with an extra sensor for detecting the marker 17. When an unmanned vehicle comes near an intersection, a marker 17 set at the intersection is detected by the extra sensor and the unmanned vehicle is forcibly decelerated by a travel control program.
However, such a countermeasure for prevention of zig-zag travel requires the marker 17 to be provided at the intersection, the extra sensor for detecting the marker 17, and a travel control program. In addition, when the layout is to be changed, the software must also be changed in a complex manner.